Urolagnia is a form of salirophilia in which sexual excitement is associated with the sight or thought of urine or urination. Some anthropologists and sociobiologists believe that breast fetishism derives from the breasts similarity to buttocks, but instead provide sexual attraction from the front of the body. Yaoi is anime or manga that features gay males . Cum shots typically do not appear in gay cock girl-girl scenes and orgasm is normally implied by utterances, cinematic conventions, or body movement. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. It has since become popular enough with couples to be discussed during an episode of Sex and the City. There are number of types of sex parties: Swinger party/gathering A swinger party or partner-swapping party is a gathering at which individuals or couples in a committed relationship can engage in sexual activities with others as a recreational or social activity. In S/M, the Sadist is usually the Top and the Masochist the Bottom, but these roles are frequently more complicated or jumbled . The activity is done by itself or as a part of or porn milf prelude to other activities which many times involve sex. As a form of non-penetrative sex, it can be done for its own enjoyment or as foreplay. Commenting on why there are not as many female macrophiles, psychologist Helen Friedman theorized that because women in most societies already view men as dominant and powerful, there no need for them to fantasize about it. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. Diaper fetishism, nappy lesbian hentai fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers. Interactive pornography, available in CD-ROM and DVD format, allows the viewer to select the particular acts performed at any one time, sometimes with the camera providing a first person view.